Separation of alkyl bromide from hydrocarbons by extractive distillation



United States Patent O 3,288,877 SEPARATEON F ALKYL BROMIDE FROM HY-DROCARBONS BY EXTRACTIVE DISTILLATION William H. Taylor and Cecil A.Newton, Houston, Tex., assignors to Petra-Tex Chemical Corporation,Houston, Tern, a corporation of Delaware No Drawing. Filed June 29,1962, Ser. No. 206,170 18 Claims. (Cl. 260-680) This invention relatesto the purification of hydrocarbon streams by the separation of alkylbromides from the hydrocarbons. More particularly, it relates to aprocess for the separation of methyl bromide from hydrocarbons of 4carbon atoms.

The use of bromine or a bromine liberating material as a catalyst forthe dehydrogenation of hydrocarbons to diolefins has been disclosed incopending applications. According to these applications, unsaturatedcompounds such as diolefins may be produced by reacting a mixture of thecompound to be dehydrogenated, oxygen and a source of bromine at anelevated temperature. The efiluent from the dehydrogenation zone orreactor comprises the unsaturated product, some unconverted feed andsmall amounts of inorganic bromides. The reactor 'efiluent also containsorganic alkyl bromides such as methyl bromide. Although these alkylbromides are present in relatively small amounts, they are seriouscontaminates in the product and are ditficult to remove. For example,the presence of the methyl bromide in the unsaturated productsignificantly affects the utility of the unsaturated products becausethe methyl bromide is corrosive and because the products are used, forexample as monomers, and the presence of methyl bromide affects thepolymerization rate of the monomer. Furthermore, methyl bromide is avaluable dehydrogenation catalyst and should be recovered in order touse it in the feed to the dehydrogenation zone.

The problem of the removal of water soluble inorganic bromides such asI-IBr and NH Br from the reactor efiluent is different from that of theremoval of methyl bromide. One distinction We have found is that methylbromide behaves similarly to the organic product and consequently cannotbe washed out with water. When a hydrocarbon efiluent contaminated withmethyl bromide is washed with water, essentially all of the methylbromide goes through with the washed hydrocarbon.

The removal of methyl bromide from the reactor effiuent is aggravatedbecause the methyl bromide may be present in relatively small amountsbased on the other possible components in the efiluent such as unreactedfeed, products such as monoolefins and diolefins, steam, nitrogen,oxygen and decomposition products. The methyl bromide compound mayamount to only a few tenths percent or less of the efiluent. We havefound that methyl bromide is particularly difficult to separate fromsuch compounds as n-butane and cis-butene-Z, and this is one reasonmethyl bromide cannot be efificiently removed from the etfiuent bydistillation.

It is an object of this invention to provide a process for theseparation of methyl bromide from hydrocarbons. It is also an object ofthis invention to provide a method for the removal of both the inorganicand organic bromides from the reactor effluent of processes involvingbromine catalysts. It is an object to reduce the total bromine contentpresent in the product in all forms to only a negligible amount. It isalso an object to provide a process for the recovery of bromine andbromine compounds from the etlluent from dehydrogenation processesutilizing bromine liberating materials as catalysts. Another object isto provide an improved process for the removal of bromine and brominecompounds from dehydrogenation processes utilizing ammonium bromide as a3,288,877 Patented Nov. 29, 1966 catalyst. It is an additional object ofthis invention to devise a process for the recovery and re-utilizationof methyl bromide in dehydrogenation processes utilizing bromineliberating catalysts. Another object is to provide a method for theseparation of methyl bromide from hydrocarbons of 4 carbon atoms, suchas butenes and butadiene. Other objects of the invention will be evidentfrom the discussion and claims which follow.

According to this invention a method has been discovered for the removalof methyl bromide from hydrocarbon compositions which contain some Chydrocar bons and which are contaminated with methyl bromide. Broadlyspeaking, the process comprises contacting the hydrocarbon streamcontaminated with methyl bromide with a particular type of organiccontacting solvent in a distillation column. The added organiccontacting solvent has a dielectric constant of at least about 10, suchas greater than 9, measured at 25 C. The organic contacting solvent mustalso have a molecular weight within the range of 35 to 225. The boilingpoint of the solvent at 760 mm. of mercury will be between 25 C. and 250C., and preferably will be between about 40 C. and or 200 C. The organiccontacting solvent preferably will not form a minimum boiling pointazeotrope with methyl bromide, and preferably Will not form a constantboiling point azeotrope with either the C hydrocarbon or the methylbromide. Ordinarily the organic contacting liquid will not contain atomsother than carbon, hydrogen, oxygen, nitrogen, sulphur, chlorine,bromine and iodine. The solvents will contain from 1 to 15 carbon atomsand will usually contain from 1 to 10 carbon atoms. The purifiedhydrocarbon stream goes oil overhead and the methyl bromide dissolved inthe added organic contacting liquid comes off as bottoms.

Processes for dehydrogenation utilizing bromine cat.- alysts aredescribed in the copending application of Laimonis Bajars and Russell M.Mantell, Serial No. 856,- 339, filed December 1, 1959, now abandoned andthe application of Richard 1. Gay, Serial No. 36,705, filed June 17,1960, now US. Patent 3,207,805. According to these processes, thecompound to be dehydrogenated together with oxygen and bromine as acatalyst is reacted at elevated temperatures to form a reaction mixturecomprising unreacted feed, the unsaturated product and various brominecompounds. The source of bromine may be either elemental bromine or anycompound of bromine which would liberate bromine under the conditions ofreaction. Suitable sources of bromine are hydrogen bromide, elementalbromine; aliphatic bromidessuch as methyl bromide, 1,2-dibromoethane,ethyl bromide, amyl bromide and allyl bromide; cycloaliphatic bromdiessuch as cy-clohexylbromide; aromatic bromides such as benzyl bromide;bromohydrins such as ethylene bromohydrin; bromine substituted aliphaticacids such as bromoacetic acid; ammonia bromide; organic amine bromidesalts such as methyl amine hydrobromide; and the like. Mixtures ofvarious bromine compounds may be used. The preferred sources of bromineare elemental bromine, hydrogen bromide, ammonium bromide, alkylbromides of one to six carbon atoms and mixtures thereof. The amount ofelemental bromine, or the equivalent amount of bromine compound, may beas little as about 0.001 or less mol of bromine per mol of hydrocarbonto be dehydrogenated, generally no more than about 0.10 mol or 0.20 molof bromine per mol of hydrocarbon to be dehydrogenated are necessary,although larger amounts such as 0.5 mol may be used.

The oxygen may be supplied by any source such as pure oxygen or as air.The amount of oxygen employed will usually be greater than 1.25 mols ofoxygen per atom of bromine. Usually the ratio of mols of oxygen to atomsof bromine will be from about 2 to 150 with the best results havingbee-n obtained at ratios between about 8 and 100 mols of oxygen per atomof bromine. Diluents such as steam, nitrogen, carbon dioxide orhydrocarbons may be included to reduce the partial pressure of thecompound to be dehydrogenated to less than equiv alent to about 10 orinche of mercury absolute at a total pressure of one atmosphere.Desirable results have been obtained utilizing from about 3 to about 30mols of steam per mol of compound to be dehydrogenated and excellentresults have been achieved with from about 5 to mols of steam per mol ofcompound to be dehydrogenated.

These processes may be conducted in the absence of contact catalysts,but better results are obtained if the reaction is conducted in thepresence of catalysts containing metal atoms of Groups IA, IB, IIA, IIB,IIIB, IVA, IVB, VA, VB, VIB, VIIB, VIII, the lanthanum series elements,thorium, uranium and mixtures thereof. The preferred catalysts arecompounds of elements of Groups IA, IIA, IIIB, IVA, IVB, VA, VB, VIB,VIIB, VIII and mixtures thereof. These groups are based on the PeriodicTable as found on pages 400-401 in the Handbook of Chemistry andPhysics, 39th (1957-5 8) edition, Chemical Rubber Publishing Co. Thesemetal atoms may conveniently be present in the forms of the elementalmetal, metal oxides, metal hydroxides, metal salts, such as the halides,or metal compounds which will be converted to these forms under theconditions of reaction. Examples of catalysts would be potassium oxide,magnesium oxide, lanthanum oxide, titanium dioxide, vanadium pentoxide,chromous oxide, manganese dioxide, ferric oxide, cobaltic chloride,nickel phosphate, cuprous phosphate, zinc phosphate, stannic phosphateand bismuth trioxide.

These processes will normally be conducted at a temperature of reactionbetween about 450 C. to about 850 C. or higher, such as about 1000 C.The temperature of reaction is measured at the maximum temperature inthe reactor. The flow rates of the reactants may be varied quite widelyand can be established by those skilled in the art. Good results havebeen obtained with flow rates of the compound to be dehydrogenatedranging from about A to 8 liquid volumes of compound per volume ofreaction zone, with the volumes of liquid calculated at standardconditions of 760 mm. of mercury absolute at C. If the reactor isunpacked, the reaction zone is defined as the portion of the reactorwhich is at a temperature of at least 400 C. If the reactor is packed,the reaction zone is defined as the volume of reactor containingpacking. The desired residence or contact time of the reactants in thereaction zone under any given set of reaction conditions depends on allthe factors involved in the reaction. Contact times such as from about0.01 to about 5 or 10 seconds have been found to give excellent results.Generally, the contact time will be between about 0.1 and one second.Contact time is the calculated dwell time of the reaction mixture in thereaction zone assuming the mols of product mixture are equivalent to themols of feed. The preferred compounds to be dehyd-rogenated arealiphatic hydrocarbons of 2 to 6 carbon atoms, which contain at leasttwo adjacent carbon atoms, each of which carbon atom has at least onehydrogen atom attached. Good results have been achieved with a feed ofat least about to mol percent of a monoethylenically unsaturatedaliphatic hydrocarbon, such as the hydrocarbons of from 4 to 5 carbonatoms containing a monoethylenically unsaturated straight chain of atleast four carbon atoms. Thus, butadiene-l,3, and vinyl acetylene may beproduced from butene-l or butene-2 or mixtures thereof, and isoprene maythe produced from any of the methyl butenes, such as Z-methyl butene-l,Z-methyl butene-2 or Z-methyl butene-3 or mixtures thereof. Isoprene mayalso be produced from methyl butanes, such as Z-methyl butane; alsoolefins and diolefins may be produced from saturated hydrocarbons, forexample, butadiene and butene may be produced from n-butane. A mixtureof monoolelins and diolefins may also be pro duced, such as a mixture ofbutadiene-l,3 and butenes from a feedstock of a mixture of n-butane andbutene. The process of this invention is particularly useful for theremoval of methyl bromide from the reactor effluent obtained from thedehydrogenation of hydrocarbons of 4 carbon atoms such as n-butane,butene-l and butene-2.

The efiiuent from the reactor may be cooled to condense the watcr of theeffluent in any conventional manner such as by the use of tube typecondensers or refrigeration. Normally, the temperature to which theeffluent is cooled will be to a temperature no greater than the boilingpoint of water under the conditions of condensation, but will not be atemperature low enough to condense the ethylenica-lly unsaturatedorganic compounds. That is, the temperature of the effiuent will becooled to a temperature of no greater than equivalent to 100 C. atatmospheric pressure.

The condensed water may be removed from the hydrocarbon vapor by theusual means known in the art such as by knock-out vessels and vaporseparators. The separated water phase will contain the inorganic brominematerials such as hydrogen bromide, elemental bromine or ammoniumbromide. Generally at least or weight percent of the inorganic brominematerials are removed prior to the treatment of the hydrocarbon phase ofthe efiiuent with the organic contacting solvent according to thisinvention.

The vapor phase from the vapor separators is usually then liquified,such as by compression, prior to further treatment to remove the methylbromide. The compressed gases may then be treated with the organiccontacting solvent in the distillation column. However, in theproduction of butadiene it is usually desirable to first remove the Cand lighter components from the mixture. The C hydrocarbons may beremoved according to techniques known in the art. One technique for theremoval of C hydrocarbons is to use an oil absorber column. In thecolumn the lean oil, such as naphtha, absorbs essentially all of the Cand higher hydrocarbons and the lighter fractions are taken oiloverhead. The fat oil from the absorber may then be stripped to removethe C and higher hydrocarbons from the oil. The overhead vapors may thenbe cooled and accumulated. The overhead from the stripper will containconcentrated butadiene contaminated with methyl bromide. In thisoverhead normally the concentration of butadiene will be at least 40 molpercent of the mixture and the methyl bromide will be less than five molprecent of the mixture. The overhead from the stripper may convenientlybe used as the stream to be treated according to this invention toremove the methyl bromides.

The organic contacting liquid is contacted with the contaminatedhydrocarbon in a distillation column. For example, the contaminatedhydrocarbon may be continuously fed to a distillation column below thepoint of entry of the organic contacting liquid. The organic contactingliquid then flows downwardly in the column and thus contacts the risingstream of contaminated hydrocarbon. The organic contacting liquidcontaining the methyl bromide is then taken oil as bottoms and thepurified hydrocarbon is taken off overhead. Any organic contactingliquid which comes ofi overhead may be separated from the hydrocarbonsuch as by distillationfii a second column to flash off the hydrocarbonoverhead. Preferably the organic contacting liquid will not be added atthe very top of the distillation column, but rather there will be someplates or packing above the inlet point for the organic contactingliquid in order that most or all of the organic contacting liquid isfractionated from the overhead vapors. Conventional distillation columnssuch as packed columns, bubble cap columns and other types known in theart may be utilized.

The operating details of the process such as temperatures at the top andbottom of the column, pressures, rate of feed of contaminatedhydrocarbon and organic contacting liquid, ratios of ingredients takenolf overhead and as bottoms, and so forth, will be dependent upon the 5process variables including the particular compositions being separatedand the organic contacting liquid selected. These particular variablesare subject to some choice. Generally the temperature at the top of thecolumn will be within the range of about C. and 125 C. and thetemperature at the bottom of the column will be in the range of about 50to 250 C. With the preferred solvents and operating conditions thetemperature at the top of the column will ordinarily be Within the rangeof C. to 75 C. and the temperature at the bottom of the column withinthe range of about 100 C. to 200 C. Pressures within the column may beatmospheric, subatmospheric or superatmospheric such as within the rangeof 0 p.s.i.g. or less to 250 p.s.i.g.

It is an advantage of this invention that the separation of the methylbromide from the hydrocarbon can be made efficiently with a relativelysmall amount of organic contacting liquid. Separation of methyl bromidemay be obtained with from about 5 to 99 mol percent organic contactingsolvent based on the total amount of C hydrocarbons in the distillationcolumn. However, it is an advantage of this invention that theseparation may made with relatively small amounts of organic contactingsolvent such as from about 5 to mol percent organic contacting solventbased upon the total amount of C hydrocarbons in the distillationcolumn.

Suitable organic contacting liquids are such as organic amides, ketones,aldehydes, alcohols, acids, acid chlorides, acid anhydrides, ethers,nitrates, nitriles, amines, heterocyclic nitrogen compounds,heterocyclic oxygen compounds, phenols, sulfoxides, sulfates,thiocyanates, aliphatic amines, halogenated aliphatic compounds, and thelike, which have the above defined characteristics. Examples ofcompounds are aliphatic aldehydes such as acetaldehyde, propionaldehydeand butyraldehyde; aro- 0 matic aldehydes such as 'benzaldehyde; mixedaliphatic and aromatic aldehydes such as p-isopropyl benzaldehyde;aliphatic monohydric alcohols such as ethanol, 1- propanol, l-butanoland l-heptanol; aliphatic polyhydric alcohols such as glycol, glycerol,1,4-butanediol and sorbitol; aromatic substituted aliphatic alcoholssuch as benzylalcohol; ether alcohols such as 2-methoxyethanol,diethylene glycol, dipropylene glycol and ethylene glycol monomethylether; halogenated alcohols such as 2-chloroethanol; alkanol amines suchas ethanol amine; aliphatic ketones such as acetone, Z-butanone,Z-pentanone, 3-pentanone, 4 methyl-Z-pentanone, diacetone alcohol,mesityl oxide, l-chloro-Z-propanone and acetonyl alcohol; cycloaliphaticketones such as cyclopentanone and cyclohexanone; aromatic ketones suchas benzophenone; mixed aliphatic and aromatic ketones such asacetophenone; halogenated aliphatic hydrocarbons such as1,2-dichloroethane and ethyl bromide; acid halides such as acetylchloride and acetyl bromide; alkyl thiocyanates such asmethylthiocyanate; aliphatic nitro compounds such as nitromethane,nitroethane, l-nitropropane, ethylene nitrate and isobutyl nitrate;aromatic nitro compounds such as nitromethane, nitroethane,l-nitropropane, ethylene nitrate and isobutyl nitrate; aromatic nitrocompounds such as nitrobenzene, o-nitrotoluene, and o-nitrophenol;aliphatic nitriles such .as acetonitrile, propionitrile,isobutyronitrile, lactic acid nitrile, 5,5-oxidipropionitrile andB-methoxypropionitrile; substituted aliphatic nitriles such asbenzonitrile; aliphatic amides such as formamide, dimethyl formamide andacetamide; aliphatic amines such as 1,2-etl1ane diamine; halogenatedaliphatic acids such as chloroacetic acid; sulfates such as methylsulfate; sulfoxides such as dimethyl sulfoxide; hydroxy substitutedaromatic compounds such as phenol, o-cresol and o-meth- 75 oxyphenol;esters such as fi-hydroxyethyl acetate, {3- ethoxyethyl acetate andglycol monoacetate; ethers such as [3,,8-dichlorodiethyl ether; acidanhydrides such as acetic anhydride; acids such as dl-lactic acid;cyanamides such as dimethyl cyanamide; heterocyclic nitrogen compoundssuch as pyridine, pyrrolidone and l-methyl-Z- pyrrolidone; heterocyclicoxygen compounds such as gamma-butyrolactone, furfural and the like.Preferred are the aliphatic and the described other types of ketonecompounds such as acetone and methylethyl ketone; dimethyl sulfoxide,dimethyl formamide and nitrobenzene. Particularly preferred is methylethyl ketone because any methyl ethyl ketone present in a stream beingrecycled to the dehydrogenation zone will be converted to butadiene.

Mixtures of the described organic contacting liquids with each other maybe employed. Furthermore, mixtures with other liquids may be elfectivelyutilized. For example, mixtures of the organic contacting liquids withsolvents of a dielectric constant of less than 9, measured at 25 C., maybe employed, such as a mixture of methylethyl ketone and benzene.Ordinarily the total amount of added organic solvent, other than thedescribed high dielectric constant organic contacting solvent, and/ orwater will be present in an amount between 1 and 50 Weight percent ofthe total solvent. Particularly desirable results may also be obtainedby the addition of water to the organic contacting liquid. Convenientlythe water will be present in an amount between about 0.5 and 25 weightpercent based on the total, but ordinarily the water will be present inan amount between 0.5 and 10 weight percent Water. Combinations such asmethylethyl ketone, benzene and water are within the scope of thisinvention. The treated hydrocarbon comes off overhead from the solventcontacting column. The purified hydrocarbon product may be furtherpurified by any of the methods known in the art for separating thesehydrocarbon mixtures. For example, if butadiene is the desired productand the treated hydrocarbon may be extractively distilled to separatethe butadiene from the remaining hydrocarbons. A normal feed to theextractive ditsillation column would comprise isobutylene, butene-l,butadiene-1,3, n-butane, trans-Z-butene and cis-2-butene. This mixtureis subjected to extractive distillation using an organic solvent such asfurfural, or an organic solvent together with water. Essentially all ofthe butadiene, and some of the 2-butenes are absorbed by the solvent,and the remainder of the C hydrocarbons are removed as overhead. Thebutadiene containing solvent may then be fed to a solvent stripper thatseparates the C hydrocarbons from the solvent. If desired, as a finalstep, the overhead product from the solvent stripper is fed to afractionating column. The Z-butenes comprise the bottom product of thiscolumn and butadiene with a purity of greater than 98 percent distillsoverhead and is collected.

Another Well known method for the purification of the butadiene is theprocess of selective absorption with a cuprous salt solution. Thebutadiene in the treated hydrocarbon overhead from the solventcontacting column may be separated by such a process. The butadiene ispreferentially absorbed in the cuprous salt solution and after the otherhydrocarbons have been stripped off, the butadiene is stripped off. Asdescribed above, the butadiene may then also be fractionated to removeresidual hydrocarbons.

The bottoms from the solvent contacting distillation column contains themethyl bromide dissolved in the organic contacting solvent, togetherwith a minor amount of hydrocarbons. The methyl bromide and thehydrocarbons may then be stripped from the organic contacting solventsuch as ina fractionating column. The methyl bromide may then beutilized in any desired manner, but it is an advantage of this inventionthat it can be recycled directly to the dehydrogenation zone to act as abromine liberating material.

The effectiveness of the process was demonstrated in distillationequipment using methyl ethyl ketone as the organic contacting solvent.For convenience, the contaminated hydrocarbon was contacted with themethyl ethyl ketone in two packed columns. The two columns wereeffectively being operated as a single column, with the bottoms from thefirst column being fed to the top of the second column and the overheadfrom the second column being fed to the still pot of the first column.Each column was about 70 feet in overall height and had an internaldiameter in the packed section of 3 feet. Each of the columns had five10 foot high sections packed with Intalox Saddle inert ceramic packing.The 10 foot sections were fitted with distribution, hold-down, and support plates. The contaminated hydrocarbon was fed to the second columnand the methyl ethyl ketone was fed to the first column.

The contaminated hydrocarbon feed contained, on a mol percent basis,about 72.2 percent butadiene, 8.5 percent cis-butene-2, 12.1 percenttrans buten-e-2, 1.4 percent n-butane, and 0.5 percent methyl bromide,together with minor amounts of carbon dioxide, ethylene, propylene,propyne, vinyl acetylene, isobutylene and C and higher hydrocarbons. Thecomposition of this feed is set forth in the table. This contaminatedhydrocarbon composition was fed to the distribution plate immediatelyabove the bottom foot section of packing in the second column. Thiscontaminated feed was fed to the second column at a rate of about 1.68barrels per hour. The temperature in the still pot of this second columnwas maintained at about 260 F. and the temperature of the overhead wasabout 137 F. The overhead from this second column was fed to the stillpot of the first packed column. The methyl ethyl ketone was fed to thedistribution plate immediately above the third section of packing fromthe top of the first column at a rate of about 2.4 barrels per hour. Thetemperature in the still pot in the first column was about 127 F. andthe temperature of the overhead was about 115 F. The overhead from thefirst column was taken off and condensed in a condenser and collected inan accumulator. A portion of the overhead was refluxed by feeding intothe top of the first column and the remainder was taken off as product.The reflux rate was 8.0 barrels per hour and the product was taken oifat the rate of about 1.28 barrels per hour. No methyl bromide wasdetected in the product. The approximate composition of the overheadproduct is shown in the table below.

The bottoms from the first column was collected in a still pot andconveyed from the still pot to the distribution plate immediately abovethe top packed section of the second column. The second column wasequipped with a reboiler in the still pot to cause the methyl ethylketone to reflux in the coliunns. The bottoms from the second columncontained methyl ethyl ketone, the methyl bro mide and some of thehydrocarbons. This bottoms was conveyed to a stripper column, at therate of about 2.8 barrels per hour. The stripper column was equippedwith a reboiler, and was a duplicate of the second column. The strippercolumn was also packed with /4 Intalox Saddles. The feed to the strippercolumn was to the distribution plate immediately above the third packedsection from the top. The hydrocarbons and methyl bromide were strippedoflt overhead from the methyl ethyl ketone. The methyl ethyl ketone wastaken off as bottoms from the stripper column and returned to the firstcolumn at the methyl ethyl ketone feed plate indicated above. The feedrate of the methyl ethyl ketone to the first column was about 2.4barrels per hour. The temperature in the still pot of the strippercolumn was about 280 F. and the temperature of the overhead from thestripper column was about 118 F. The overhead from the stripper columnwas condensed and collected in an accumulator. About 6.0 barrels perhour of this accumulated overhead was refluxed to the stripper column,and about 0.4 barrel per hour was taken off as stripper overheadproduct. The overhead from the stripper contained the methyl bromidetogether with some of the hydrocarbons and a small amount of methylethyl ketone. The composition of the stripper overhead is indicated inthe table. The overhead from the stripper was fed to the inlet to thedehydrogenation reactor where the methyl bromide acted as a catalyst andthe methyl ethyl ketone was converted to butadiene.

TABLE Contami- Product nated (Overhead Stripper Hydro- First; 0 verheadcarbon, COlUIILH), M01 Percent Mol Percent M01 Percent Methane and C0 0.18 C 's 0. 05 CO2 and Cg'S 0.02 Methyl Acetylene 0. 04 Isa-butane 0. 10I-butane 1. 44 Butene-L 4. 26 Isobutylene- 0. 29 Cis-hutene-2 8. 46Trans-butene-2 12. 08

Butadiene-L3 72. 18 Ethyl Acetylene." 0.02 Vinyl Acetylene 0. 26 C andhigher D. 08 Methyl bromide 0. 54

The applicability of various organic contacting solvents includingmethyl ethyl ketone was demonstrated in a small scale laboratoryapparatus. The effect of the addition of solvents to a mixture to beseparated in a distillation column can be demonstrated by anexperimental determination of the relative volatilities,which are knownas the alpha values. The alpha values were determined by the equilibriumtechnique. According to this technique a composition corresponding tothat which is to be separated in a distillation column is enclosed in acontainer under such conditions that there will be a liquid phase and avapor phase. After equilibrium has been reached, the vapor phase and theliquid phase are both analyzed to determine the relative amounts of eachcomponent in the vapor phase and in the liquid phase. The alpha valuefor the separation of components A and B is then calculated using thefollowing relationship:

The run is then duplicated with the exception that the solvent for whichthe effect is to be determined is also added to the container. The alphavalue of the new composition is then determined and compared to thatobtained without the added solvent. In these examples the standardhydrocarbon blend composition to be separated consisted of, by molepercent, 8.68% n-butane, 4.55% trans-butene-Z, 4.63% cis-butene-2,73.03% bu tadiene-1,3, 3.72% vinylacetylene and 5.39% methyl bromide.The apparatus consisted of a cc. glass pres sure bottle equipped with astandard metal cap with a neoprene liner and 2 entry holes punched inthe top. The bottle was capped and evaporated to 0.3 mm. mercury. Thedescribed liquid hydrocarbon blend composition was then added in aWeighed quantity by means of a hydropermic syringe. The liquid phasecomprised about 100 cc. The pressure bottle was then placed in aconstant temperature bath of F. The bottles were allowed to come toequilibrium in 3 hours. While still in the bath, a sample of the vaporwas analyzed chromotographically and calculated as mole percent. Therelative volatilities between methyl bromide and the various Chydrocarbons were calculated, for example, with butadiene-L3.

(Mole percent butadiene in vapor) (mole percent methyl bromide inliquid) The values thus obtained were the standard values. Runs werethen made by the same procedure except that the various solvents wereadded. The solvent to be tested was added in an amount so as to comprise20 mole percent of the total mixture. The total volume in the pressurebottle was regulated so that it was about 100 cc. as in the control run.The results obtained using various solvents according to this inventionare shown in the table. The eifectiveness of each solvent for theseparation of methyl bromide from butadiene can be determined by thedeviation of the alpha value from the alpha value of 0.891 obtainedbetween methyl bromide and butadiene in the absence of any solvent. Theefiectivness of each solvent for the separation of methyl bromide fromeach of n-butane, trans-butene-2 and cis-butene-2 can similarly bedetermined by the deviation of the alpha values from the respectivealpha values of .885, 1.017 and 1.151 respectively between methylbromide and each of these C hydrocarbons. For example, the alpha valueof .470 between methyl bromide and n-butane in the presence of dimethylsulfoxide may be compared with the alpha value of .885 in the absence ofsolvent. This significant lowering of the alpha value by dimethylsulfoxide shows that dimethyl sulfoxide is an effective contactingsolvent for the separation of methyl bromide from, for example, nbutane.

The approximate dielectric constants of these contacting solvents are asfollows: methyl ethyl ketone, 18.5 at 20 C.; dimethyl sulfoxide 45;acetonitrile, 37.5 at 20 C.; l-butanol, 17.1 at 25 C.; dimethylformamide, 37.7 at 20 C.; furfural, 41 at 20 C.; and nitrobenzene, 34.8at 25 C.

butene-l, butene-Z, vinyl acetylene and mixtures of these unsaturatedhydrocarbons, such as a composition containing at least a total of 50mol percent of unsaturated C hydrocarbons based on the total hydrocarbonphase. Another example of a composition containing methyl bromide whichcould be separated according to this invention would be that obtainedwhen 2-methyl pentene-2 is cracked to isoprene, and the product containssome C.; hydrocarbons.

We claim:

1. A process for separating methyl bromide from aliphatic hydrocarbonsof 4 carbon atoms comprising unsaturated hydrocarbons, said methylbromide being present in an amount of less than 25 mol percent based onthe C hydrocarbons present, which comprises fractionally distilling thesaid aliphatic hydrocarbons while feeding to the distillation an organiccontacting solvent having from one to 15 carbon atoms and not havingatoms other than carbon, hydrogen, oxygen, nitrogen, sulphur, chlorine,bromine and iodine, said organic contacting solvent having a dielectricconstant at 25 C. of at least about 10, a boiling point of about 25 C.to 250 C., and a molecular weight of at least 35, with a purifiedaliphatic hydrocarbon stream being taken ofr overhead from thedistillation and the methyl bromide being dissolved in the said organiccontacting solvent taken off as a bottoms.

2. A process for separating methyl bromide from a mixture of aliphatichydrocarbons of 2 to 6 carbon atoms, said mixture containinghydrocarbons of 4 carbon atoms, comprising unsaturated hydrocarbons,said methyl bromide being present in an amount of less than 25 molpercent based on the C hydrocarbons present, which comprises distillingthe said aliphatic hydrocarbons while feeding to the distillation anorganic contacting solvent having from one to 15 carbon atoms and nothaving atoms other than carbon, hydrogen, oxygen, nitrogen, sulphur,chlorine, bromine and iodine, said organic con- TABLE.ALPHA VALUESBETWEEN METHYL BROMIDE AND 04 HYDROCARBONS Effect of Organic ContactingSolvents N0 Dirnethyl Methyl Dimethyl Aceto- Nitro- Solvent SulfoxideEthyl l-Butanol Formamide Furfural nitrile benzene Ketone a-Methylbromide/n-butane 885 470 713 780 600 587 633 619 a-Methyl bromide/transbutene 1. 017 607 829 909 731 755 807 790 1. 151 692 922 1. 036 821 851903 908 Although the process for the removal of methyl bromide has beendescribed utilizing the efiluent from a process for the dehydrogenationof hydrocarbons with bromine liberating materials, the invention isapplicable to other processes where similar compositions are to beseparated. Generally, the organic mixture to be separated will containat least a total of 10 mol percent of C hydrocarbon, and the process ismost useful when the composition contains at least about 40 or molpercent C hydrocarbons. Normally, most of the hydrocarbons in the totalcomposition containing the methyl bromide will have from 2 to 6 carbonatoms. Other components such as water, nitrogen, oxygen, bromine and soforth may be present also. The mol percent methyl bromide present mayvary, but will normally be less than 25 mol percent of the amount of Chydrocarbons present. It is an advantage of this invention that theprocess is useful in separating organic compositions in which the methylbromide is present in an amount of less than 5 mol percent, such as lessthan 2 mol percent, based on the total C.; hydrocarbons present.Preferably, the mixture from which the methyl bromide is separated willcontain at least one compound selected from the group consisting ofbutadiene-1,3,

tacting solvent having a dielectric constant at 25 C. of at least about10, a boiling point of about 25 C. to 250 C. and a molecular Weight ofat least 35, with a purified aliphatic hydrocarbon stream being takenoff overhead from the distillation and the methyl bromide beingdissolved in the said organic contacting solvent taken oil as a bottoms.

3. A process for separating methyl bromide from aliphatic hydrocarbonsof 4 carbon atoms comprising unsaturated hydrocarbons, said methylbromide being present in an amount of less than 5 mol percent based onthe C hydrocarbons present, which comprises fractionally distilling thesaid aliphatic hydrocarbons while feeding to the distillation an organiccontacting solvent having from one to 15 carbon atoms and not havingatoms other than carbon, hydrogen, oxygen, nitrogen, sulphur, chlorine,bromine and iodine, said organic contacting solvent having a dielectricconstant at 25 C. of at least 9, a boiling point of about 25 C. to 250C., and a molecular Weight of at least 35, with a purified aliphatichydrocarbon stream being taken off overhead from the distillation andthe methyl bromide being dissolved in the said organic contactingsolvent taken off as a bottoms.

4. A process for separating methyl bromide from aliphatic hydrocarbonsof 4 carbon atoms containing butadiene-1,3, said methyl bromide beingpresent in an amount of less than 5 mol percent based on the Chydrocarbons present, which comprises fractionally distilling the saidaliphatic hydrocarbons while feeding to the distillation an organiccontacting solvent having from one to 15 carbon atoms and not havingatoms other than carbon, hydrogen, oxygen, nitrogen, sulphur, chlorine,bromine and iodine, said organic contacting solvent having a dielectricconstant at 25 C. of at least about 10, a boiling point of about 40 C.to 200 C. and a molecu lar Weight of at least 35, with a purifiedaliphatic hydrocarbon stream being taken off overhead from thedistillation and the methyl bromide being dissolved in the said organiccontacting solvent taken off as a bottoms.

5. A process for separating methyl bromide from unsaturated aliphatichydrocarbons of 4 carbon atoms, said methyl bromide being present in anamount of less than 5 mol percent based on the C hydrocarbons present,which comprises fractionally distilling the said aliphatic hydrocarbonsin contact with from 5 to 35 mol percent, based on the total amount ofsaid aliphatic hydrocarbons, of methyl ethyl ketone, with a purifiedaliphatic hydrocarbon stream being taken off overhead from thedistillation and the methyl bromide being dissolved in the methyl ethylketone taken off as bottoms.

6. A process for separating methyl bromide from unsaturated aliphatichydrocarbons of 4 carbon atoms, said methyl bromide being present in anamount of less than 5 mol percent based on the C hydrocarbons present,which comprises fractionally distilling the said aliphatic hydrocarbonsin contact with from 5 to 35 mol percent, based on the total amount ofsaid aliphatic hydrocarbons, of dimethyl sulfoxide, with a purifiedaliphatic hydrocarbon stream being taken off overhead from thedistillation and the methyl bromide being dissolved in the dimethylsulfoxide taken off as bottoms.

7. A process for the preparation of unsaturated aliphatic hydrocarbonsby dehydrogenation which comprises heating a mixture of a 4 carbonaliphatic hydrocarbon to be dehydrogenated and a bromine liberatingcatalyst at an elevated temperature in a dehydrogenation zone, toproduce an effluent comprising unsaturated aliphatic hydrocarbon andmethyl bromide, said methyl bromide being present in an amount of lessthan 25 mol percent based on the C hydrocarbons present, and separatingthe methyl bromide by fractionally distilling said efiluent whilefeeding to the distillation an organic contacting solvent having fromone to 15 carbon atoms and not having atoms other than carbon, hydrogen,oxygen, nitrogen, sulphur, chlorine, bromine and iodine, said organiccontacting solvent having a dielectric constant at 25 C. of at leastabout 10, a boiling point of about 25 C. to 250 C. and a molecularweight of at least 35, with a purified aliphatic hydrocarbon streambeing taken off overhead from the distillation and the methyl bromidebeing dissolved in the said organic contacting solvent taken off as abottoms.

8. A process for the preparation of unsaturated aliphatic hydrocarbonsby dehydrogenation which comprises heating a mixture of an aliphatichydrocarbon to be dehydrogenated and an ammonium bromide catalyst at anelevated temperature in a dehydrogenation zone, to produce an eflluentcomprising unsaturated aliphatic hydrocarbon and methyl bromide, saidmethyl bromide being present in an amount of less than 5 mol percentbased on the C hydrocarbons present, and separating the methyl bromideby fractionally distilling said efiluent while feeding to thedistillation an organic contacting solvent having from one to 15 carbonatoms and not having atoms other than carbon, hydrogen, oxygen,nitrogen, sulphur, chlorine, bromine and iodine, said organic contactingsolvent having a dielectric constant at 25 C. of at least about 10, aboiling point of about 25 C.

12 to 250 C. and a molecular weight of at least 35, with a purifiedaliphatic hydrocarbon stream being taken 01f overhead from thedistillation and the methyl bromide being dissolved in the said organiccontacting solvent taken ofi as a bottoms, and returning the said methylbromide to the dehydrogenation zone as a catalyst.

9. A process for the preparation of unsaturated aliphatic hydrocarbonsby dehydrogenation which comprises heating a mixture of an aliphatichydrocarbon to be dehydrogenated, steam and a bromine liberatingcatalyst at an elevated temperature in a dehydrogenation zone, toproduce an effluent comprising unsaturated aliphatic hydrocarbon, steamand methyl bromide, said methyl bromide being present in an amount ofless than 2 mol percent based on the C hydrocarbons present, condensingout steam to form an aqueous phase, separating said aqueous phase fromthe remaining organic phase, and separating the methyl bromide byfractionally distilling said organic phase while feeding to thedistillation an organic contacting solvent having from one to 10 carbonatoms and not having atoms other than carbon, hydrogen, oxygen,nitrogen, sulphur, chlorine, bromine and iodine, said organic contactingsolvent having a dielectric constant at 25 C. of at least about 10, aboiling point of about 25 C. to 250 C. and molecular weight of at least35, with a purified aliphatic hydrocarbon stream being taken 01foverhead from the distillation and the methyl bromide being dissolved inthe said organic contacting solvent taken off as a bottoms, andreturning bromine to the dehydrogenation zone as a catalyst.

10. A process for the preparation of butadiene-1,3 by dehydrogenation ofbutene which comprises heating a mixture of butene and a bromineliberating catalyst at an elevated temperature in a dehydrogenationzone, to produce an effluent comprising butene, butadiene-l,3 and methylbromide, said methyl bromide being present in an amount of less than 25mol percent based on the C hydrocarbons present, and separating themethyl bromide by fractionally distilling said efiiuent in contact withan aliphatic ketone having a dielectric constant at 25 C. of at least 10and av boiling point between 40 C. and 200 C., with a purified aliphatichydrocarbon stream being taken ofi overhead from the distillation andthe methyl bromide being dissolved in the aliphatic ketone taken off asbottoms, and returning the said methyl bromide to the dehydrogenationzone as a catalyst.

11. A process for the preparation of unsaturated aliphatic hydrocarbonsof 4 carbon atoms by dehydrogenation which comprises heating a mixtureof a 4 carbon aliphatic hydrocarbon to be dehydrogenated and a bromineliberating catalyst at an elevated temperature in a dehydrogenation zoneto produce an effiuent comprising a 4 carbon unsaturated aliphatichydrocarbon and methyl bromide, said methyl bromide being present in anamount of less than 25 mol percent based on the C hydrocarbons present,and separating the methyl bromide by fractionally distilling saidefiluent in contact with an organic contacting solvent, said organiccontacting solvent being methyl ethyl ketone, with a purified aliphatichydrocarbon stream being taken off overhead from the distillation andthe methyl bromide being dissolved in the methyl ethyl ketone taken oldas bottoms, and returning the said methyl bromide to the dehydrogenationzone as a catalyst.

12. A process for the preparation of unsaturated aliphatic hydrocarbonsof 4 carbon atoms by dehydrogenation which comprises heating a mixtureof a 4 carbon aliphatic hydrocarbon to be dehydrogenated and a bromineliberating catalyst at an elevated temperature in a dehydrogenation zoneto produce an effluent comprising a 4 carbon unsaturated aliphatichydrocarbon and methyl bromide, said methyl bromide being present in anamount of less than 25 mol percent based on the C hydrocarbons present,and separating the methyl bromide by fractionally distilling saideffluent in contact with an organic contacting solvent, said organiccontacting solvent being dimethyl sulfoxide, with a purified aliphatichydrocarbon stream being taken off overhead from the distillation andthe methyl bromide being dissolved in the dimethyl sulfoxide taken oifas bottoms, and returning the said methyl bromide to the dehydrogenationzone as a catalyst.

13. A process for the preparation of unsaturated aliphatic hydrocarbonsof 4 carbon atoms by dehydrogenation which comprises heating a mixtureof a 4 carbon aliphatic hydrocarbon to be dehydrogenated and a bromineliberating catalyst at an elevated temperature in a dehydrogenation zoneto produce an efiluent comprising a 4 carbon unsaturated aliphatichydrocarbon and methyl bromide and separating the methyl bromide byfractionally distilling said efiluent in contact with an organiccontacting solvent, said organic contacting solvent being dimethylformamide, with a purified aliphatic hydrocarbon stream being taken offoverhead from the distillation and the methyl bromide being dissolved inthe dimethyl formamide taken off as bottoms, and returning the saidmethyl bromide to the dehydrogenation zone as a catalyst.

14. A process for the preparation of unsaturated aliphatic hydrocarbonsof 4 carbon atoms by dehydrogena tion which comprises heating a mixtureof a 4 carbon aliphatic hydrocarbon to be dehydrogenated and a bromineliberating catalyst at an elevated temperature in a dehydrogenationzone, to produce an effluent comprising a 4 carbon unsaturated aliphatichydrocarbon and methyl bromide and separating the methyl bromide byfractionally distilling said efiluent while feeding to the distillationan organic contacting solvent having from one to carbon atoms and nothaving atoms other than carbon, hydrogen, oxygen, nitrogen, sulphur,chlorine, bromine and iodine, said organic contacting solvent having adielectric constant at 25 C. of at least about 10 and a boiling point ofbetween about 40 C. and 200 C., and being selected from the groupconsisting of aliphatic ketones, aromatic ketones, aliphatic sulfoxides,aliphatic nitriles, aromatic nitriles, aliphatic amides, aliphaticaldehydes, heterocyclic oxygen compounds and mixtures thereof, with apurified aliphatic hydrocarbon stream being taken off overhead from thedistillation and the methyl bromide being dissolved in the said organiccontacting solvent taken off as a bottoms, and returning bromine to thedehydro genation zone as a catalyst.

15. A process according to claim 14 wherein the said organic contactingsolvent is methyl ethyl ketone.

16. A process for the preparation of bntadiene-1,3 which comprisesheating a gaseous mixture of butene, oxygen, steam, ammonium bromide andmethyl bromide to a temperature of at least 400 C. in a dehydrogenationzone to produce a gaseous dehydrogenation zone eifiuent containinghydrocarbons, steam, ammonium bromide, hydrogen bromide, elementalbromine and methyl bromide, cooling the dehydrogenation zone effluent tocondense the steam into an aqueous phase containing elemental bromineand inorganic compounds thereof, separating from the gaseous mixture ofhydrocarbons the condensed aqueous phase containing ammonium bromide,hydrogen bromide and elemental bromine; liquifying the remaining gaseousmixture of hydrocarbons and methyl bromide; separating the methylbromide by fractionally distilling the resulting liquified mixture ofhydrocarbons and methyl bromide while feeding to the distillation anorganic contacting solvent having from one to 15 carbon atoms and nothaving atoms other than carbon, hydrogen, oxygen, nitrogen, sulphur,chlorine, bromine and iodine, said organic contacting solvent having adielectric constant at C. of at least about 10, a boiling point of about25 C. to 250 C. and a molecular weight of at least 35; separating thedissolved methyl bromide from the contacting solvent and returning themethyl bromide to the dehydrogenation zone as a catalyst, with apurified aliphatic hydrocarbon stream being taken off overhead from thedistillation and the methyl bromide being dissolved in the said organiccontacting solvent taken off as a bottoms.

17. A process for the preparation of butadiene-1,3 which comprisesheating a gaseous mixture of butene, oxygen, steam and ammonium bromideto a temperature of at least 400 C. in a dehydrogenation zone to producea dehydrogenation zone effluent, cooling the dehydrogenation zoneeffluent to condense the steam into an aqueous phase containingelemental bromine and inorganic compounds thereof, separating from theremaining gaseous mixture of hydrocarbons and methyl bromide thecondensed aqueous phase containing ammonium bromide, hydrogen bromideand elemental bromine; liquifying the mixture of hydrocarbons and methylbromide, and separating the methyl bromide by fractionally distillingthe resulting liquified mixture in contact with an organic contactingsolvent, said organic contacting solvent being methyl ethyl ketone in anamount from about 5 to 35 mol percent based on the amount ofhydrocarbons in the distillation column, with a purified aliphatichydrocarbon stream being taken off overhead from the distillation andthe methyl bromide being dissolved in the methyl ethyl ketone taken offas bottoms, and returning the said methyl bromide to the dehydrogenationzone as a catalyst.

18. A process for the preparation of butadiene-1,3 which comprisesheating a gaseous mixture of butene, oxygen, steam and ammonium bromideto a temperature of at least 400 C. in a dehydrogenation zone to producea dehydrogenation zone effluent, cooling the dehydrogenation zoneeffluent to condense the steam into an aqueous phase containingelemental bromine and inorganic compounds thereof, separating from theremaining gaseous mixture of hydrocarbons and methyl bromide thecondensed aqueous phase containing ammonium bromide, hydrogen bromideand elemental bromine; liquifying the mixture of hydrocarbons and methylbromide, and separating the methyl bromide by fractionally distillingthe resulting liquified mixture in contact with an organic contactingsolvent, said organic contacting solvent being dimethyl sulfoxide in anamount from about 5 to 35 mol percent based on the amount ofhydrocarbons in the distillation column, with a purified aliphatichydrocarbon stream being taken oif overhead from the distillation andthe methyl bromide being dissolved in the dimethyl sulfoxide taken offas bottoms, and returning the said methyl bromide to the dehydrogenationzone as a catalyst.

References Cited by the Examiner UNITED STATES PATENTS 2,357,028 8/1944Shiras et al 203-57 3,219,546 11/1965 Fannin et al 260652 X FOREIGNPATENTS 807,149 1/ 1959 Great Britain.

OTHER REFERENCES Weissberger: Distillation-Technique of OrganicChemistry, vol. IV, published by Interscience Pub., Inc., New York,1951, pages 338340,

PAUL M. COUGHLAN, JR., Primary Examiner. DANIEL E. WYMAN, Examiner.

1. A PROCESS FOR SEPARATING METHYL BROMIDE FROM ALIPHATIC HYDROCARBONSOF 4 CARBON ATOMS COMPRISING UNSATURATED HYDROCARBONS, SAID METHYLBROMIDE BEING PRESENT IN AN AMOUNT OF LESS THAN 25 MOL PERCENT BASED ONTHE C4 HYDROCARBONS PRESENT, WHICH COMPRISES FRACTIONALLY DISTILLING THESAID ALIPHATIC HYDROCARBONS WHILE FEEDING TO THE DISTILLATION AN ORGANICCONTACTING SOLVENT HAVING FROM ONE TO 15 CARBON ATOMS AND NOT HAVINGATOMS OTHER THAN CARBON, HYDROGENS, OXYGEN, NITROGEN, SULPHUR, CHLORINE,BROMINE AND IODINE, SAID ORGANIC CONTACTING SOLVENT HAVING A DIELECTRICCONSTANT AT 25*C. OF AT LEAST ABOUT 10, A BOILING POINT OF ABOUT 25*C.TO 250*C., AND A MOLECULAR WEIGHT OF AT LEAST 35, WITH A PURIFIEDALIPHATIC HYDROCARBON STREAM BEING TAKEN OFF OVERHEAD FROM THEDISTILLATION AND THE METHYL BROMIDE BEING DISSOLVED IN THE SAID ORGANICCONTACTING SOLVENT TAKEN OFF AS A BOTTOMS.